Rigorous G&G Science Underpinning the Project

July 2011By Susan R. Eaton

American Association of Petroleum Geologists (AAPG)

Aeromagnetic, gravity and reflection seismic data were integrated with refraction seismic data – on both conjugate margins of the North Atlantic – to unravel the Scotian Margin’s history of rifting and drifting.

In 2009, deploying 100 multi-component ocean bottom seismometers, the group acquired a 400-kilometer-long refraction seismic line across the Scotian Basin and the northeastern end of the East Coast Magnetic Anomaly (ECMA), a pronounced feature previously thought to delineate the northern limit of the basin’s rift footprint.

The refraction line, shot in a dip orientation, imaged the Moho at an estimated depth of 40 kilometers.

Investigators noted the existence of seaward dipping seismic reflectors along the entire Scotian Margin and across the Atlantic Ocean, in Morocco, suggesting the margin’s volcanic origin – and they interpreted a high velocity feature on the 2009 refraction line, pointing to the existence of a continuous, “under-plated body.”

In other words, the ECMA doesn’t terminate because of reduced volcanic activity – rather, its magnetic signature is masked by an increased thickness of the overlying sedimentary package.

But what does this tectonic analysis mean for oil and gas exploration?

Geologists say it confirms that a volcanic margin runs along the entire length of the Scotian Basin to the southern Grand Banks, setting up a broad tectonic and depositional fairway for the development of an extensive Lower Jurassic source rock.

‘Bonanza’ Potential

Integrating all of these diverse data sets was a monumental task undertaken by Paris-based Beicip-Franlab – the data were fed into a 3-D petroleum systems modeling package, leading to a predictive basin model for petroleum reservoir facies, source rocks and seals.

The model calculated both qualitative and quantitative hydrocarbon volumes and associated risk factors for each of the six geographical zones, tripling the yet-to-find resource estimates (121 Tcf of natural gas and eight billion barrels of oil) for offshore Nova Scotia in the process.

The study’s final compilation, aPlay Fairway Atlas consisting of 300-plus plates, is available for free to industry.

Hamish Wilson

“An oil company can take the Atlas and start prospecting in the basin with the 10 horizons that are internally consistent and rigorously checked,” said AAPG member Hamish Wilson, program director of the PFA study and principal advisor with RPS Energy Ltd., Henley-on-Thames, England.

“We set out to find reasons why the oil industry should come back to Nova Scotia,” Wilson continued, pointing to global competition in “hot” exploration areas on the West African conjugate margin. “We thought we might have to try to make a silk purse out of a sow’s ear.”

But based on the study’s results, Wilson, like others, is bullish about the area’s potential.

“I believe that our optimism is warranted,” he said. “There’s a rigorous science underpinning this Play Fairway Analysis.

“There’s clearly a play risk here,” he continued, “but the seismically mapped structures are big enough, and there’s source rock.